Biomedical Engineering Reference
In-Depth Information
Table 2.1 Materials for hip and knee joint replacement
Material
Hip replacement
Knee replacement
Hip stem Femoral Cup/ Metal
Femoral
Tibial Tibial Patella
(uncemented) head
insert
back component plate cushion
shell
CP Ti
±
±
±
X
±
±
±
±
Ti alloys
X
±
±
X
X
X
±
±
CoCr
X
X
X(M)
X
X
X
±
±
alloys
Stainless
±
X
±
±
±
±
±
±
steel
Alumina
±
X
X(C)
±
±
±
±
±
Zirconia
±
X
±
±
±
±
±
±
UHMWPE
±
±
X
±
±
±
X
X
CP Ti: commercially pure titanium; UHMWPE: ultrahighmolecular weight polyethylene.
X: clinically used. ±: clinically not used or not successful; M: metal-on-metal bearing; C: ceramic-
on-ceramic bearing.
2.1.2 Cemented and cementless hip replacements
Hip replacements can be cemented, cementless, or hybrids. For cemented hip
replacements, the clinically used stem materials include stainless steel and
cobalt±chromium alloys. The most often used bone cement is polymethyl-
methacrylate (PMMA). The success of a cemented hip implant depends on both
a strong bone±cement bonding and a stable cement±prosthesis interface. Though
cemented hip replacements have been generally considered as a good fixation
option, there is concern about implant loosening. This could occur when
surrounding cemented fractures over time lead to wear debris particle generation
(from both the cement itself and polyethylene socket); such events cause
inflammation which further causes osteolysis (bone destruction and resorption)
and instability of the implant (loosening).
Because of this, cementless hip replacements have been developed to
eliminate PMMA-related mechanism of failure. Both titanium and cobalt±
chromium alloys are used in cementless hip stems. Initial stability and fixation of
cementless hip implants can be achieved by press-fitting the component and
using screws, spikes, and pegs. However, the long-term stability and fixation of
cementless femoral and acetabular components rely on adequate osseointegration
onto and into the implant. For this purpose, stem surfaces are mostly textured or
roughened to allow intimate bony apposition and provide long-term implant
anchorage. They can also be made porous or coated with bioactive ingredients to
enhance bone ingrowth. Metal-backed shells of acetabular cups in cementless hip
replacements also have a porous or coated surface to promote bone ingrowth.
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